Water Storage Update

The news continues to improve on the water storage front. Today’s update from the California Department of Water Resources shows a nice jump in storage over the past week at Lake Oroville, the largest component of storage in the State Water Project.
Normally at this time of year, we would be happy with the storage leveling off. That makes this week’s climb — along with that of the past several weeks — all the more encouraging. We have now almost reached the storage level of three years ago.
Let’s contrast this year’s graph (dark blue line) with two other years, starting with 2006-2007 (pink line). The 2006-2007 storage peaked on about April 1; we have yet to reach peak storage this year — a full two months later.
In contrasting this year with 2005-2006 (black line), we see the two graphs are nearly parallel. This means that the rate of storage increase is nearly identical — although we remain about 1 million acre-feet behind 2005-2006. As a reminder, that deficit is about the same as three completely full Castaic Lakes, so we’re still way behind our storage of four years ago.
This year’s graph actually looks slightly steeper than 2005-2006 — an excellent sign. Also, in that previous year, storage hit the maximum allowed in the lake — but that limit will not influence this year’s situation. Also in 2005-2006, the decline in storage began just before July 1. It will be interesting to watch the “decline” date this year.
Two factors are working in our favor. First, the above-average snowfall, coupled with the late and cool Spring, means that the inflow to Oroville will continue well into the Summer.
Second, outflow may be reduced because of too much storage at Oroville’s “sister” reservoir, Lake Shasta. The US Bureau of Reclamation, operators of Shasta, are releasing higher than normal amounts of flow, in anticipation of possible flooding conditions during the late snow melt. Shasta is 97% full, which is 113% of normal for this time of year. In addition to providing a water supply, recreation, and environmental outflows, major reservoirs like Shasta and Oroville are the principal tools of flood control. But a full reservoir cannot function as a flood control tool, so Shasta is actually draining a bit of their storage on purpose, just in case the snow melt comes all at once. This could cause a flooding event, and they need to be prepared.
Both Shasta and Oroville discharge into the Sacramento River. If this river is already running high due to discharges from Shasta, there is less pressure on Oroville to release water. So, inflow may continue to exceed outflow at Oroville for another few weeks, thus allowing for additional storage gains.
Of course, water in storage does not necessarily translate into water supply for cities and farms around the State — such water must be pumped out of the Sacramento River delta, and environmentally-directed restrictions on this pumping continue to restrict water supplies.
Two more notes today: first, it’s election day, so get out there and vote! Second, I will probably be “silent” for the next few days, due to other scheduling commitments — no, not another camping trip!

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